When taking pictures a photographer controls the focus distance by using various tenses or by adjusting the shutter size and/or lens distance from the point in the camera that records the picture. The focus distance is the distance from the camera in which objects are maximally focused relative to the rest of the picture. Around the focus distance is an area which is essentially focused at least above a certain threshold level. The picture can be adjusted to have certain areas focused and certain areas blurred, for example an object at a specific distance can be focused with everything else blurred. Alternatively, the picture can be focused from a specific distance, up to a specific distance or between two distances. Typically the focused area with a reasonable level of clarity is referred to as the depth of field.
In some cases the required depth of field cannot be achieved with the camera being used, for example to have an image focused with a blurred background generally requires a wide shutter opening that is not available on simple cameras (e.g. point and shoot cameras). Alternatively, it may be desired to have the entire image focused when the lighting is poor, the focusing requires a small shutter opening whereas the lighting requires a large shutter opening or long exposure time.
Generally, once the picture is taken the ability to change the focal distance of the picture is very limited. In recent years with the growth in digital imaging various techniques have been proposed to improve images. Some techniques use image processing methods to achieve better focused images. Other techniques use special optics to collect more light during the picture shoot and then digitally process the image to achieve a sharper image.
U.S. Pat. No. 7,003,177 describes the use of multi-exposure techniques to provide an image with an extended depth of field.
U.S. Pat. No. 6,876,763 describes a method of improving the resolution of an image using a color mosaic sensor.